1. Field of the Invention
This invention relates to a method of reading a mark and an apparatus for the same in which a mark formed on a functional device formation body where predetermined functional devices are formed on a base is optically read.
2. Description of the Related Art
A magnetic head slider used when recording/reproducing data on/from an information recording media such as a fixed disk device is generally fabricated using a photolithography technique, a thin film formation technique, an etching technique, a polishing process technique and the like as follows: A plurality of thin film magnetic head devices is formed on a wafer and the wafer is cut so as to be separated into individual magnetic head sliders, each of which includes at least one of the thin film magnetic head device.
When manufacturing a large quantity of magnetic head sliders, an identification mark is provided on a predetermined surface of each magnetic head slider through a series of manufacturing processes. This identification mark provides, for example, manufacturing information of the magnetic head slider, such as date manufactured, manufacturing specifications, material used, manufacturing number and the like. The identification mark is provided for the purpose of managing the manufacturing history of the magnetic head slider. With mass-manufacturing, process management utilizing manufacturing information provided through the identification code makes it possible to avoid confusion of products with different manufacturing specifications and to keep track of the number of manufactured products and the whole manufacturing process accurately. When a defective part is used in a product during the manufacturing process, or when a product fails in performance or the like is found after completing the manufacturing process, a scale of occurrence of the defect is quickly and accurately detected and the defective products are effectively removed by performing a performance evaluation or the like for every identification code of a series of products manufactured.
Here, examples of the identification mark generally provided are an identification mark constituted with a string of character symbols as an arrangement of characters or numbers (called as a xe2x80x9ccharacter symbolxe2x80x9d hereinafter) and an identification mark constituted with a graphical pattern as an arrangement of predetermined graphics. As to the identification mark constituted with the string of character symbols, a single character symbol or a combination of a plurality of character symbols indicates the specific manufacturing information. As to the identification mark constituted with the graphical pattern, the number, shape, size, arrangement or the like of the graphical symbols indicates the specific manufacturing information.
An example of a method of providing the identification mark on the magnetic head slider and a method of forming the identification mark is a method in Japanese Patent Laid-open No. Hei 9-50606 applied by this applicant. In this bulletin, two types of ultra-minute identification marks, where one is constituted with a string of character symbols and the other is constituted with a graphical pattern, are provided on a surface of a magnetic head slider, on the surface thin film magnetic head devices being formed, to indicate manufacturing information of the magnetic head slider. In this case, the identification code constituted with the string of character symbols is formed simultaneously with a magnetic layer as a part of the thin film magnetic head device, whereas the identification mark constituted with the graphical pattern is formed on a predetermined region on a protection film formed on the surface of the thin film magnetic head by irradiating a laser.
The ultra-minute identification mark provided on the magnetic head slider is visually identified using a microscope or the like by a worker or the like. The identification mark is just an arrangement of characters and graphics, so the identification mark is converted into corresponding manufacturing information by the worker or the like using a conversion chart. If needed, conversion may be performed more than once. In this way, the necessary identifying information is obtained from the identification mark provided on the magnetic head slider.
The above-described conventional method of reading the identification mark of the magnetic head slider has the following problems to be improved.
First, with the conventional method of reading the identification mark, onerous work such as the recognition of the ultra-minute identification mark, conversion into the manufacturing information or the like needs to be performed using manpower. Therefore, conducting the work requires a lot of time, which is a great obstacle to improvement of productivity.
Second, recognition of the ultra-minute identification mark, conversion into the manufacturing information, and the like are performed using manpower, so that there exists the risk of a mistake caused by human error such as a mistake in reading character symbols and a mistake in counting numbers of graphical symbols when recognizing the identification mark, a mistake in conversion from the identification number into the manufacturing information or the like.
In the semiconductor field, for example, as in Japanese Patent Laid-open No. Hei. 8-130171, No. Hei 7-141461 and No. Hei 6-52138, a technique to optically read the identification mark provided on each semiconductor wafer is disclosed, for example.
In these bulletins, the technique for reading the identification mark is disclosed on the assumption that the identification mark is formed on a semiconductor wafer itself, i.e., a base where semiconductor devices are formed. However, as in the aforementioned Japanese Patent Laid-open No. Hei 9-50606 applied by this applicant, a technique for reading the identification mark formed on a portion, for example, a part of the thin film magnetic head device or the protection film other than the base has not been disclosed. Further, the above three bulletins regarding a semiconductor process are described based on the premise that the identification mark is read in a wafer process and there is no description with regard to management of the identification information after the base is separated into individual members (semiconductor chip).
This invention is designed to overcome the aforementioned problems. It is an object of the invention to provide a method of reading a mark and an apparatus for the same in which even a mark formed on a portion other than a base in a functional device formation body such as a magnetic head slider can be accurately and quickly read.
According to the invention, the method of reading a mark, formed on a functional device structure layer or a protection layer in a functional device formation body including at least a base, the functional device structure layer including a predetermined functional device structure formed on the base through a thin film process and the protection layer covering the functional device structure layer, the method includes steps of irradiating an illumination light of an normal incident illumination onto the functional device formation body and reading the mark formed on the functional device structure layer or the protection layer based on a reflected light from the functional device formation body.
Here, the xe2x80x9cfunctional device structurexe2x80x9d is a device structure having a predetermined function including a magnetic, electric, optic function such as a magnetic recording/reproducing device structure, a semiconductor device structure, an optical recording/reproducing structure, or the like. Examples of the xe2x80x9cfunctional device formation bodyxe2x80x9d are a magnetic head slider wherein a magnetic recording device or a magnetic reproducing device are formed, a semiconductor chip wherein a semiconductor device is formed, an optical pickup wherein an optical recording/reproducing device is formed or the like. The xe2x80x9cmarkxe2x80x9d denotes an object of perception used to show certain things. Examples of the xe2x80x9cmarkxe2x80x9d are not only symbols but also languages or letters. The xe2x80x9cperfect incident illuminationxe2x80x9d is an illumination method employing an optical system similar to a telecentric optical system (not a perfect telecentric optical system). Specifically, with this illumination method an illumination light vertically comes onto a surface to be irradiated and the reflected light becomes parallel to the light axis not only on the light axis but outside of the light axis as well. Similarly, at any point between the condenser lens behind the iris of telecentric and the surface of an image, the reflected light becomes parallel to the light axis on the light axis as well as outside of the light axis.
With the method of reading a mark of the present invention, the mark can be formed to include the manufacturing information which is referred to in the manufacturing process of the functional device formation body. In this case, preferably the mark includes origin identifying information which shows the origin of the base included in the functional device formation body. Here, the xe2x80x9corigin identifying informationxe2x80x9d is information showing the origin of the base in the manufacturing process. For instance, when the base is separated from a predetermined mother material, the origin identifying information includes information specifying the mother material, manufacturing lot information of the mother material, and information of the position where the base is located in the mother material or the like.
With the method of reading a mark of the invention, the mark can include at least a dot pattern constituted with a plurality of dots and a character symbol. In this case, preferably the dot pattern is formed of a residue of material melted on the protection layer by an irradiation of a predetermined energy beam. The dot pattern may be an irradiation scar caused by deterioration of a part of the protection layer by the irradiation of the energy beam. In these cases, preferably the mark includes the origin identifying information to represent the origin of the base included in the functional device formation body as described.
With the method of reading a mark of the invention, the character symbol is formed simultaneously with a predetermined layer which is a part of the functional device structure layer. In this case, the character symbol includes address information representing an address of the base in the parent material from which the base included in the functional device formation body has been separated.
With the method of reading a mark of the invention, preferably the step for reading the mark includes a process for generating an image data by photoelectrically converting a reflected light from the functional device formation body, a process for obtaining an image pattern by performing image recognition based on the formed image data and a process for obtaining information corresponding to the image pattern based on the obtained image pattern.
With the method of reading a mark of the invention, the functional device structure can be a thin film magnetic head structure for performing at least one of recording and reproducing information to/from a recording medium.
According to the invention, the apparatus for reading a mark, included in a functional device formation body including at least a base, a functional device structure layer having a predetermined functional device structure formed on the base through a thin film process, a protection layer covering the functional device structure layer and the predetermined mark formed on the functional device structure layer or the protection layer, are provided with a light source for irradiating a light, a normal incident illumination system for making it possible to irradiate an illumination light of a normal incident illumination onto the functional device formation body, and means of reading the mark formed on the functional device structure layer or the protection layer based on a reflected light from the functional device formation body.
With the method of reading a mark and the apparatus for the same, the illumination light of the normal incident illumination is irradiated onto the functional device formation body and the mark formed on the functional device structure layer or the protection layer is read based on the reflected light from the functional device formation body.
Other and further objects, features and advantages of the invention will appear more fully from the following description.